The following invention relates to increasing the stability of vertical GMR (VGMR) heads and, in particular, to a method for stabilizing the free layers in VGMR heads using antiferromagnetic materials.
Referring to FIG. 1, there is shown a prior art giant magneto-resistive (GMR) sensor 2, also called a spin valve (SV) sensor, used for reading magnetically encoded data from the surface of magnetic media. SV sensor 2 includes a layered stack that is sensitive to the changing magnetic fields originating from a storage medium. The layered stack includes a free magnetic layer 4, a non-magnetic Cu layer 6, a pinned magnetic layer 8 and a pinning layer 10 that fixes the magnetic orientation of pinned magnetic layer 8. In operation, the changing magnetic fields originating from the magnetic storage medium produce a change in the magnetization direction of free magnetic layer 4 with respect to pinned magnetic layer 8 and thereby changes the resistance of SV sensor 2. This change in resistance is sensed to indicate the information stored on the magnetic medium.
A known problem associated with SV sensors is that they often xe2x80x9cfracturexe2x80x9d into multiple magnetic domains when exposed to an external magnetic field creating what is called xe2x80x9cBarkhausen-noisexe2x80x9d that adversely affects the stability and sensitivity of the SV sensor. To maximize the SV sensor""s performance, it is desirable to maintain the GMR stack in a single domain state using a process known as boundary control stabilization.
A number of methods exist for stabilizing a SV sensor in a single domain state. For example, in FIG. 1, SV sensor 2 is stabilized using antiferromagnetic (AFM) exchange coupling in which the wing areas of free magnetic layer 4 is pinned by AFM layers 12,12xe2x80x2 and the center portion of free magnetic layer 4 is the xe2x80x9cactivexe2x80x9d sensing area. Thus, AFM exchange coupling creates a single state in the GMR stack thereby eliminating the noise associated with domain activity.
Another prior art method used to stabilize SV sensors is hard biasing in which a permanent magnet is positioned adjacent to the active area of the GMR stack in order to boundary control stabilize the active area of the GMR stack.
Yet other methods exists for stabilizing SV sensors including permanent magnet (PM) ferromagnetic coupling and configuring the GMR stack according to advantageous geometries.
Referring now to FIG. 2, there is shown a VGMR head 14 capable of supporting much greater track densities than GMR heads. Unlike SV heads, VGMR heads have a GMR stack 16 in which both magnetic layers are free and respond to the external magnetic fields emanating from the magnetic media. In VGMR head designs both free layers have to be kept in a single domain configuration in order to achieve electrical stability. Due to geometric restraints, however, the prior art stabilization techniques used for SV sensors are unsuitable for VGMR sensors (see A. V. Pohm, et. Al., IEEE Tran. Magn. 33, 2392 (1997)).
A prior art method for stabilizing VGMR heads, as shown in FIG. 2, is to use hard edge stabilization (see A. V. Pohm, et. Al., IEEE Tran. Magn. 34, 1486 (1998)). In hard edge stabilization, the edges of the free magnetic layers are placed adjacent the air bearing surface (ABS) and are used to sense the changing magnetic fields of the magnetic media. Because the coercitivity of the edges of the free layers is higher than their center areas, hard edge stabilized VGMR heads demonstrate improved stability.
Using hard edge stabilization to stabilize VGMR heads, however, has several drawbacks. First, for reasons not well understood, hard edge stabilization is difficult to realize. Also, while hard edge stabilization improves the stabilization of the VGMR head, it does completely stabilize the head. Furthermore, hard edge stabilized VGMR heads are difficult to produce in volume. It has been found that, in volume production, hard edge stabilized VGMR heads have only a 50% stability yield, which is an unacceptably low rate.
Accordingly, it is desirable to provide a method for stabilizing the free magnetic layers in VGMR heads that is suitable for volume production.
The present invention is directed to overcoming the drawbacks of the prior art. Under the present invention a stabilized vertical GMR head is provided and includes a GMR stack having a pair of free magnetic layers and having a first edge and a second edge. A pair of soft magnetic layers is also included and positioned so that one of the soft magnetic layers is adjacent to the first edge of the GMR stack and another of the soft magnetic layers is adjacent to the second edge of the GMR stack. A pair of AFM layers are included and positioned so that one of the AFM layers is adjacent to one of said soft magnetic layers and another of said AFM layers is adjacent to the other of said soft magnetic layers. Thus, by positioning the AFM layers in such a manner, a vertical GMR head is provided in which the free magnetic layers are stabilized and that is suitable for volume production.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims. Other features and advantages of the invention will be apparent from the description, the drawings and the claims.